Power analysis indicated that a total sample size of 46 patients (23 patients in each cohort) would provide a statistical power of 99% with a 2-sided a level of 0.05 to detect significant differences in the visual analog scale (VAS) score at 6 hours postoperatively, assuming an effect size of 0.88 (mean difference, 2.46, standard deviation, 2.8). This was based on the mean and standard deviation of the VAS at 6 hours postoperatively observed in a pilot study of 20 patients.